Apparatus for combustion analysis



O 1962 E. L. BENNET 3,058,814

APPARATUS FOR COMBUSTION ANALYSIS Filed Aug. 15, 1959 2 Sheets-Sheet 1 oxrssv 4 r l unmm VIII/Ill!!! [Ill/[41,7

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Oct. 16, 1962 E. BENNET 3,058,814

APPARATUS FOR COMBUSTION ANALYSIS Filed Aug. 15, 1959 2 Sheets-Sheet 2 12 2 .34 v -44 PDWE INVENTOR.

United States Patent O 3,053,814 APPARATUS FOR COMBUSTION ANALYSIS Eugene L. Bennet, St. Joseph, Mich, assignor to Laboratory Equipment Corporation, St. Joseph, Mich, a corporation of Michigan Fiied Aug. 13, 1959, Ser. No. 833,486 6 Claims. (Cl. 23-253) The present invention relates to analytical chemistry, and more particularly to the quantitative determination of carbon or sulfur in analytical samples by combustion of the sample in oxygen followed by analysis of the gaseous products of combustion for carbon dioxide or sulfur dioxide respectively.

In general, in combustion analysis methods, a small weighed quantity of steel or other combustible material to be analyzed for its carbon or sulfur content is burned in an atmosphere of substantially pure oxygen, and the gaseous products of combustion are drawn off into apparatus which determines the carbon dioxide or sulfur dioxide content of the gas. The gas analyzing apparatus which receives the products of combustion may be of any of several familiar types, such as an Orsat apparatus, or a gravimetric or conductometric apparatus, or a sulfur titrator. Such gas analysis apparatus needs no description here, since the present invention is concerned with combustion of the sample rather than with the analysis of the gas thus produced.

One of the objects of the present invention is to provide an improved apparatus for the controlled, non-explosive burning of a sample of steel or other material so as to convert the sample into products of combustion extremely quickly such that a quantitative determination for carbon or sulfur may be carried out without delay and at low cost.

Yet another object is to provide novel apparatus for accomplishing the above by controlled combustion with a small quantity of oxygen so that the total quantity of combustion gases, which include principally carbon dioxide, sulfur dioxide, and an excess of oxygen, will be held to a practical minimum.

Still another object is to provide an improved combustion apparatus for this purpose which is reliable and which may be used with facility by technicians with a minimum of training.

7 Yet another object is to provide improved apparatus for accomplishing the combustion analysis of samples which are not easily burned, such as tungsten carbide or asbestos or clay for instance.

A further object is to accomplish all of the above with extremely low cost apparatus which, if desired, may be easily portable.

Other objects and advantages will become apparent from the following description of a preferred embodiment of my invention which is illustrated in the accompanying drawings.

In the drawings, in which similar characters of reference refer to similar parts throughout the several views,

FIG. 1 is a vertical sectional view through the essential portion of combustion apparatus which includes the features of the present invention;

FIG. 2 is a horizontal sectional view which may be considered as taken in the direction of the arrows subst-antially along the line 22 of FIG. 1, showing the major portion of the apparatus in top elevation;

FIG. 3 is a vertical sectional view taken at right angles to the view of FIG. 1, as indicated by the arrows at the ends of the line 3-3 of FIG. 2;

FIG. 4 is a fractional vertical sectional view of a portion of the apparatus illustrated in FIG. 3, with certain of the parts therein shown in an alternative position which 358i4 Patented Oct. 16, 1962 ice is assumed when the combustion chamber is opened for the insertion of a sample to be analyzed; and

FIG. 5 is a diagrammatic representation of the electrical system which comprises a portion of the apparatus.

The customary practice in chemical analysis procedures for the determination of carbon or sulfur which is based upon combustion is to burn the sample in the presence of oxygen and then to pass the products of combustion to suitable quantitative measuring apparatus where the quantity of the carbon dioxide or sulfur dioxide in the mixture can be determined. If the combustion is complete, the quantity of carbon dioxide or sulfur dioxide may be assumed to be representative of the quantity of carbon or sulfurain the original sample.

In general, two arrangements are now in use for burning such samples. The older of these consists in placing the sample to be burned in a small ceramic boat, which is then placed in a horizontal ceramic tube heated in an electric resistance furnace to a high temperature. While the boat is in this environment, oxygen is caused to flow through the tube and over and around the boat so as to come into contact with the sample. This process is continued until the sample is entirely burned, and the result ing gas is then tested for carbon dioxide or sulfur dioxide.

This method is comparatively slow, and has recently been largely replaced by a system of the type forming the subject matter of United States Patent No. 2,809,100, issued October 8, 1957, to George J. Krasl for Combustion Analyzer. In this more recent approach to the problem, the sample to be burned is placed in a small barrel-shaped crucible which is located inside a vertically positioned artificial fused quartz tube at the center of a radio frequency induction coil. Energization of the field producing coil causes heating of the sample which burns in an oxygen atmosphere.

The present apparatus and method are in some respects generally similar to the system explained in the beforementioned Krasl patent, but differs considerably therefrom primarily, from the practical standpoint, in requiring much less complex and expensive apparatus, and is based upon the fundamental discovery that under certain conditions samples of steel or iron, or even non-combustible substances, can be reliably burned in an oxygen environment without supplying additional heat from the outside, once ignition has taken place.

Referring more particularly to the drawings, the device is of small size and may be placed upon a table in close association to the gas analysis apparatus which is to be used therewith. The device shown is provided with a generally circular base 10 which has a cylindrical recess 12 in the top face at the center to receive the lower end of a synthetic quartz combustion tube 14. This combustion tube is relatively thin-walled and has a nominal internal diameter of about 1% inch. At the top of the recess 12 the metal forming the base is tapered outwardly as at 16, and this tapered shoulder is opposed by a downwardly facing similar shoulder 18 in a top plate 20.

When the top plate 20 is pressed downwardly against the base plate 10, the tapered shoulders 16 and 18 act to deform a pliable 0 ring 22 against the external surface at the lower end of the combination tube 14 so as to form a seal between the lower end of the combustion tube and the base plate 10.

The upper portion of the combustion tube 14 is shaped inwardly to provide a smaller diameter gas inlet tube 24 which, at its lower end, is partially closed, as at 26, so that the interior of the small tube 24 is connected to the main portion of the combustion chamber 14 only by a single relatively small diameter jet forming orifice 2.8. The small diameter tube 24 is relatively short and con stitntes a fitting for connection to a length of plastic tubing 30 leading to a source of oxygen supply which will 3 usually comprise an oxygen bottle together with the usual pressure regulating and flow regulating valves, a device for measuring the flow rate, and a train for the removal of impurities.

The top plate 20, which seals the O ring about the lower end of the combustion tube 14 when this top plate is pressed downwardly against the base plate 10, is normally moved upwardly so as to release the ring 22 by coil spring 32 contained within recesses 34 in the base plate 10, so that their upper ends press against the plate 22. The top plate 20 is located and its upward movement is limited by screws 35 which are threaded into the base plate and which pass through openings '37 in the top plate.

With the pressure upon the 0 ring 22 thus released, the combustion tube 14 may be pulled outwardly from the center thereof so as to open the combustion chamber. When it is desired to close the combustion chamber, the lower end of the tube 14 is pushed downwardly through the center of the O ring 22, after which a pair of overcenter toggle clamps 36 are actuated to press the top plate 20 downwardly against the bottom plate 10 so as to seal the combustion chamber.

The recess 12 beneath the lower end of the combustion tube is connected by a drilled passage 38 to a fitting 40 connected to a tube 42 leading to the gas analysis apparatus which, as previously mentioned, may be of any suitable type.

The recess 12 in the upper surface of the base plate 10 is coaxial with a second recess 44 formed in the base plate lower surface so as to form a partition or web 46 between the recesses 12 and 44. The upper surface of this partition, at its center, supports a pedestal 48 (made preferably of a ceramic material) which at its upper end supports a miniature crucible 50 of the generally cylindrical type which has its top opening directly beneath the jet forming orifice 28. This crucible is equipped with a pair of diametrically opposite electrically conductive terminal strips 52 which extend downwardly to the bottom of the crucible on the inside. At their lower ends they are interconnected by a narrower strip 54, for a purpose to be discussed presently, which extends across the bottom \of the crucible. At their upper ends, the terminal strips 52 are bent outwardly so as to pass across the top edge of the crucible and, at their outer ends, are bent downwardly to provide tabs 56 against the outer cylindrical face of the crucible 50.

These tabs 56 are opposite each other across the diameter of the crucible, and when the crucible is in position upon the pedestal 48 the tabs are clamped between a pair of spring metal leaves 58 which extend downwardly, and at their lower ends are connected to screws 60. These screws extend through the partition 46, at least one of them being insulated from the metal of the partition, with their lower ends secured by nuts to a pair of insulated leads 62 which pass outwardly through a drilled passage 64 extending between the recess 44 and the edge of the base.

The leads 62, as is best seen in FIG. 5, are connected to the secondary 64 of a transformer 66, the primary 68 of which is connected through a push button switch 70 to the electric power supply, such as a 115-volt A.C. circuit for instance. The transformer 66 in the embodiment shown has characteristics such that when the switch 70 is closed, there will be a potential across the secondary circuit of 16 to 18 volts, with a capacity of approximately 20 amperes. In a portable apparatus, a low voltage battery of suitable capacity may, of course, be substituted for the transformer.

The terminal strips 52-56 may be formed of thin sheet brass or other suitable (preferably carbon free) material, and are preformed as shown in FIG. so that they may easily be attached to the crucible in the manner described. To facilitate this attachment, particularly to facilitate insuring that the tabs 56 are at opposite sides of the crucible, it is convenient to provide the interconnecting portion 54 of narrower section as an integnal portion of the strip. Stated diilerently, it has been found that if separate terminal strips 52 are provided, one or the other of them is likely to slide around the crucible so that they are not in diametrically opposite position. By attaching the two together by the strut 54, this problem is obviated since the two terminal strips 52 can be handled as an integral unit.

The apparatus is used for the analysis of steel or iron for carbon in the following manner. One of the crucibles 50 is supplied with one of the terminal strip assemblies 525456, after which it receives the sample. The sample will ordinarily comprise one gram of iron or steel which is carefully weighed prior to being dumped into the crucible. To this is added about one gnam of tin which aids combustion and fluxing.

The crucible with its sample charge is then placed in combustion position, and this is accomplished as follows. The clamping levers 36 are moved to the relaxed position, as is indicated in FIG. 4 so as to permit the springs 32 to urge the plate 20 upwardly thereby relieving the confining pressure upon the O ring 22. The combustion tube 14 is then lifted out and laid to one side, after which the spring metal strips 58 are slightly spread with the fingers so as to permit the insertion of the crucible 50 between them. This is done in such manner that the bottom of the crucible rests upon the top of the pedestal 48 with the ears 56 of the terminal strips 52 clamped between the spring metal members 58. After this has been accomplished, the combustion tube 14 is pushed downwardly into the center of the O ring 22, after which the over-center levers of the mechanism 36 are moved to clamping position so as to squeeze the 0 ring 22 about the lower end of the combustion tube 14, thereby sealing the tube to the base plate 10.

At any time thereafter the oxygen may be turned on so that it flows downwardly through the tube 30 and through the jet forming orifice 28 so as to cause a jet of the oxygen to blow directly into the top of the crucible 50 and against the sample charge therein. After impinging against the charge so as to produce high turbulence in its vicinity, the oxygen finds its way out of the top of the crucible, into the combustion chamber, and thence downwardly into the recess 12, from which it passes outwardly through the passage 38, and hence to the gas analysis apparatus. I have found that a flow rate of about 1 /2 to 3 liters per minute is appropriate, although slightly different flow rates may work better with different materials. For instance, I have found that the optimum flow rate with the particular apparatus shown for steel is about 1 /2 liters per minute, whereas for cast iron it is about 2% liters per minute.

After the oxygen flow has been established, the button 70 is pressed so as to energize the transformer 66. This produces a relatively heavy current through the ter minal strips 52 and connecting strip 54. Because the connecting strip 54 is narrower than the main portion of the strips 52 it will almost instantly burn out, and in so doing may ignite the charge of cast iron or steel within the crucible. If it does not, there will 'be a heavy conduction of current between the terminal strips 52 by way of the iron or steel particles which will result in many of the particles being heated to the ignition point. This action takes place extremely quickly so that it is necessary to hold the switch 70 closed only momentarily. Once ignition has taken place, the switch 70 is opened, since the combustion of the iron or steel and tin in the oxygen atmosphere is sufficiently exothermic to insure that all of the sample will be burned completely in the turbulent oxygen atmosphere.

If it is desired to analyze materials which burn with considerable difiiculty, or which are non-combusti-blesuch as tungsten carbide or asbestos or clays, for instancethe crucible charge should consist of about one gram of iron chips, which serve as fuel, along with the tin and a one gram sample of the material to be analyzed. When this technique is used, it will of course be necessary to determine the blank to be subtracted from the result, this blank being determined simply by running a determination with the amount of the iron chips and tin to be used for fuel to aid the combustion of the sample to be analyzed.

Repeated tests of this apparatus under practical operating conditions demonstrate that all of the carbon and sulfur in the sample is burned, and as pointed out previously, an external energy source is required only long enough to bring about ignition of the sample in the oxygen atmosphere, after which the heat of the chemical reaction itself is sufficient to insure complete combustion.

In order to accomplish these results it is necessary that the oxygen jet be blown against the sample in the crucible with sufficient force to insure a high order of turbulence, and therefore a high rate of combustion. The velocity need not, however, be so great as to endanger any of the sample material being blown out of the crucible prior to the time it is ignited. *Once combustion is started, small burning particles may fly upwardly, but, in the oxygen atmosphere, combustion of these particles will be completed almost instantly even though they have be come detached from the main mass of the sample at the bottom of the crucible.

From the above description of a preferred embodiment of my invention it will be appreciated that variations in the apparatus and specific procedure outlined may be made without departing from the scope or spirit of the invention, and that the scope of the invention is to be determined from the scope of the following claims.

Having described my invention, what I claim as new and useful and desire to secure by Letters Patent of the United States is:

1. In combustion apparatus for chemical analysis of metallic samples, means providing a closed combustion chamber, a miniature crucible adapted to contain a sample to be analyzed disposed within said combustion chamber, said combustion chamber having a connection for the supply of oxygen thereto, the last said connection being formed to provide a single small diameter jet of oxygen directed downwardly into the center of said crucible against the sample therein so as to produce a highly turbulent oxygen atmosphere in the immediate vicinity of said sample, means providing a connection for removing gaseous products of combustion from said combustion chamber, the last said means being adapted for connection to gas analysis apparatus, a pair of electric terminal means extending downwardly into said crucible at opposite sides thereof so as to be in contact with the sample in said crucible, and electric circuit means having means within said combustion chamber for electrically contacting said terminal means for momentarily energizing said terminals at a low potential difference so as to heat the sample in said crucible to the ignition temperature by electric conduction therethrough.

2. In combustion apparatus for chemical analysis, means providing a closed combustion chamber, an open top crucible adapted to contain a sample to be analyzed disposed within said combustion chamber, said combustion chamber having a connection for the supply of oxygen thereto, the last said connection being formed to provide a jet of oxygen directed downwardly into the center of said crucible against the sample therein so as to produce a highly turbulent oxygen atmosphere in the immediate vicinity of said sample, means providing a connection for removing gaseous products of combustion from said combustion chamber, the last said means being adapted for connection to gas analysis apparatus, means providing a pair of electrically conductive terminals adjacent the interior bottom surface of said crucible so as to be in contact with a sample in said crucible, said terminals having portions extending across the top edge of said crucible to the outside surface thereof to form contacts upon the external surface of said crucible, and electric circuit means including clamping members within said combustion chamber for engaging said contacts for momentarily energizing said terminals at a low potential difference.

3. In combustion apparatus for chemical analysis, means providing a closed combustion chamber, a miniature crucible adapted to contain a sample to be analyzed disposed within said combustion chamber, said combustion chamber having a connection for the continuous supply of oxygen thereto, means providing a connection for removing gaseous products of combustion from said combustion chamber, the last said means being adapted for connection to gas analysis apparatus, a pair of spaced apart electric terminal means at the inside bottom of said crucible disposed so as to be in contact with the sample in said crucible, and electric circuit means having means within said combustion chamber for electrically contacting said terminal means for momentarily electrically energizing said terminal means.

4. In combustion apparatus for chemical analysis, means providing a closed combustion chamber, an open top miniature crucible adapted to contain a sample to be analyzed disposed within said combustion chamber, said combustion chamber having a connection for the supply of oxygen thereto, the last said connection being formed to provide a jet of oxygen directed downwardly into the center of said crucible against the sample therein so as to produce a highly turbulent oxygen atmosphere in the immediate vicinity of said sample, means providing a connection for removing gaseous products of combustion from said combustion chamber, the last said means being adapted for connection to gas analysis apparatus, means providing a pair of electrically conductive terminals adjacent the interior bottom surface of said crucible so as to be in contact with a sample in said crucible, said terminals having portions extending across the top edge of said crucible to the outside surface thereof to form contacts upon the external surface of said crucible, and electric circuit means including clamping members within said combustion chamber for engaging said contacts for momentarily energizing said terminals at a low potential difference, said clamping members also being adapted to lend support to said crucible to hold said crucible in place in said combustion chamber in a position beneath said jet forming means.

5. In combustion apparatus for chemical analysis of analytical samples, means providing a closed combustion chamber, a miniature crucible adapted to contain a sample to be analyzed disposed within said combustion chamber, said combustion chamber having a connection for the continuous supply of oxygen thereto, the last said connection being formed to provide a single small diameter jet of oxygen directed downwardly into the center of said crucible against the sample therein so as to produce a highly turbulent oxygen atmosphere in the immediate vicinity of said sample, means providing a connection for removing gaseous products of combustion from said combustion chamber, the last said means being adapted for connection to gas analysis apparatus, an integral metal strip extending downwardly into said crucible at one side,' across the bottom thereof, and up the other side in a generally U-shaped conformation, the central portion of said strip extending across the bottom of said crucible having less current capacity than the remaining end portions of said strip, and electric circuit means having means within said combustion chamber for electrically contacting opposite ends of said strip for momentarily energizing said strip at low potential so as to melt the central portion of said strip of less current capacity thereby to provide a pair of spacedapart electrically energized terminals at the inside bottom of said crucible.

6. A miniature crucible for combustion analysis of analytical samples comprising, means providing a ceramic receptacle of generally cylindrical shape with a closed bottom and open top, a pair of spaced-apart electrically conductive terminals loosely disposed within said receptacle at the bottom thereof, a structural conductive element of low current carrying capacity physically connecting said terminals to hold said terminals in fixed spaced relation, a pair of spaced apart contacting members located exteriorly of said receptacle, electrically conductive means connecting one of said contacting members to one of said terminals and the other of said contacting members to the other of said terminals, and said contacting members, said conductive means, said terminals, and said structural connecting element all comprising portions of a single unitary strip of metal.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN COMBUSTION APPARATUS FOR CHEMICAL ANALYSIS OF METALLIC SAMPLES, MEANS PROVIDING A CLOSED COMBUSTION CHAMBER, A MINIATURE CRUCUBLE AND ADAPTED TO CONTAIN A SAMPLE TO BE ANALZED DISPOSED WITHIN SAID COMBUSTION CHAMBER, SAID COMBUSION CHAMBER HAVING A CONNECTION FOR THE SUPPLY OF OXYGEN THERETO, THE LAST SAID CONNECTION BEFIG - 01 ING FORMED TO PROVIDE A SINGLE SMALL DIAMETER JET OF OXYGEN DIRECTED DOWNWARDLY INTO THE CENTER OF SAID CRUCIBLE AGAINST THE SAMPLE THEREIN SO AS TO PRODUCE A HIGHLY TURBULENT OXYGEN ATMOSPHERE IN THE IMMEDIATE VICINITY OF SAID SAMPLE, MEANS PROVIDING A CONNECTION FOR REMOVING GASEOUS PRODUCTS OF COMBUSTION FROM SAID COMBUSTION CHAMBER, THE LAST SAID MEANS BEING ADAPTED FORR CONNECTION TO GAS ANALYSIS APPARATUS, A PAIR OF ELECTRIC TERMINAL MEANS EXTENDING DOWNWARDLY INTO SAID CRUCIBLE AT OPPOSITE SIDES THEREOF SO AS TO BE IN CONTACT WITH THE SAMPLE IN SAID CRUCIBLE, AND ELECTRIC CIRCUIT MEANS HAVING ING MEANS WITHIN SAID COMBUSTION CHAMBER FOR ELECTRICALLY CONTACTING SAID TERMINAL MEANS FOR MOMENTARILY ENERGIZING SAID TERMINALS AT A LOW POTENTIAL DIFFERENCE SO AS TO HEAT THE SAMPLE IN SAID CRUCIBLE TO THE IGNITION TEMPERATURE BY ELECTRIC CONDUCTION THERETHROUGH. 